The four primary types of vertebrate tissues are epithelial tissue, muscle tissue, nerve tissue, and connective tissue. Connective tissues are typically involved in structure and support, and are usually derived from mesoderm cells. Connective tissue is widespread in the body, and as the name implies, it primarily serves a connecting function to bind or strengthen organs or other tissues. It also functions inside the body to divide and compartmentalize other tissue structures.
In vertebrates, the most common type of connective tissue is loose connective tissue. Loose connective tissue holds organs in place and attaches epithelial tissue to other underlying tissues. Loose connective tissue is named based on the “weave” of its constituent fibers. There are three main component types of loose connective tissue: collagenous fibers, elastic fibers, and reticular fibers. Collagenous fibers are made of collagen and consist of bundles of fibrils that are coils of collagen molecules. Elastic fibers are made of elastin and are stretchable. Reticular fibers join connective tissues to other tissues. Loose connective tissue also includes adipose tissue that stores fat.
Another type of connective tissue is fibrous connective tissue, which is found in tendons and ligaments. Fibrous connective tissue is composed of large amounts of closely packed collagenous fibers. Cartilage is a form of fibrous connective tissue that is composed of closely packed collageous fibers in a rubbery gelatinous substance called chondrin. The skeletons of sharks are composed of cartilage. Cartilage also provides flexible support for certain structures in humans including the nose, trachea, ears, and articulating joints, for example.
Bone and blood are two other specialized connective tissues. Bone is a type of mineralized connective tissue that contains collagen and calcium phosphate, a mineral crystal. Calcium phosphate gives bone its firmness. Blood is also considered a type of connective tissue. Even though it has a different function in comparison to other connective tissues it does have an extracellular matrix. The matrix is the plasma and erythrocytes, leukocytes and platelets are suspended in the plasma.
The connective tissues of humans and animals are constantly subjected to stresses and strains from mechanical forces and from diseases that can result in afflictions, such as arthritis, joint inflammation stiffness and connective tissue injuries such as tendonitis, bursitis, strained or torn ligaments and tendons and the like. Indeed, connective tissue afflictions are quite common, presently affecting millions of Americans. Further, such afflictions can be not only painful but, in their extreme, debilitating.
Arthritic diseases, characterized by pain, inflammation and stiffness of the joints leading to reduced range of mobility, are due to the degradation of connective tissue (mainly cartilage) in joints. Such diseases particularly affect weight-bearing joints such as the hips, knees, spine, ankles and feet and those joints with frequent movement such as hands, arms and neck. For instance, osteoarthritis (OA) in particular is a degenerative disease of the joint cartilage resulting in narrowing of the joint space and changes in the underlying bone (Barclay, et al., The Annals of Pharmacotherapy, (May, 1998) 32: 574-79). Osteoarthritis is the most common form of arthritis and it affects approximately one in ten people in North America. Osteoarthritis is not limited to humans, but occurs in other mammals such as horses, dogs, cats, mice and guinea pigs as well, making osteoarthritis one of the most common sources of chronic pain seen by veterinarians.
In humans, rheumatoid arthritis (RA) is a connective tissue disease that has some similar symptoms to osteoarthritis. Rheumatoid arthritis is among the most debilitating of all forms of arthritis, causing joints to ache and throb and eventually become deformed. Sometimes these symptoms make even the simplest daily activities difficult to manage.
The exact cause of rheumatoid arthritis is unknown, however, it is believed to be an autoimmune disease (Maini, et al., Aetiopathogenesis of Rheumatoid Arthritis. in Mechanisms and Modes of Rheumatoid Arthritis, (1995) Academic Press Ltd. pp. 25-46), in which the immune system attacks body tissues, e.g., the synovium, as if they were foreign invaders, culminating in inflammatory and destructive responses in joints as well as other tissues. It has also been postulated that rheumatoid arthritis is triggered by an infection, possibly a virus or bacterium in people with an inherited susceptibility. Some researchers also believe that hormones may be involved in the development of rheumatoid arthritis.
As with other forms of arthritis, rheumatoid arthritis involves inflammation of the joints. In rheumatoid arthritis, white blood cells, whose usual job is to attack unwanted invaders, such as bacteria and viruses, move from the bloodstream into the synovium. Here, these blood cells appear to play an important role in causing the synovial membrane to become inflamed (synovitis). This inflammation results in the release of proteins that, over months or years, cause thickening of the synovium. These proteins can also damage cartilage, bone, tendons and ligaments. Gradually, the joint loses its shape and alignment and eventually, it may be destroyed.
Under normal conditions, the body maintains the synovial joint in state of homeostasis through a variety of complex hormonal and mechanical feedback mechanisms. Several types of insult or injury can upset the delicate homeostatic balance. For example, repeated trauma or stress (slow chronic insult) to the joint during everyday use, e.g., athletic training or performance, is often the inciting cause of joint inflammation and loss of homeostasis. Initially, such stress results in only soft tissue inflammation in the form of synovitis or capsulitis (e.g., traumatic synovitis). Cartilage damage may or may not initially be present in the early stages of stress related injury or inflammation. However, the release of inflammatory mediators into the joint such as prostaglandins, cytokines, lysosomal enzymes and free radicals can lead to damage of articular cartilage and can cause cartilage degradation and leading to development of degenerative joint disease (DJD).
A second type of insult or injury, the osteochondral defect, e.g., a chip fracture, is often associated with an acute mechanical failure or traumatic injury, e.g., an acute racing or training injury, although, such a fracture can be due to secondary complications associated with chronic DJD. Under this scenario, the lesion often starts as a traumatically induced defect in the articular cartilage. This may occur as a fragmentation of the original tissue from the joint margins or other defect which compromises the surface and integrity of the articular cartilage. Exposure of the supporting subchondral bone to synovial fluid and the intermittent pressures of the synovial fluid generated by repeated joint movement (repeated stress and trauma of training or racing) can lead to progressive subchondral bone sclerosis and eventual dislodging of the chip or bone fragment. Left untreated, the resulting damage often becomes progressive and DJD results (see, e.g., Nixon et al., “EQUINE FRACTURE REPAIR”, W. B. Saunders Co., 1996 (ISBN 0-7216-6754-6)).
Under either scenario, once compromised, the damage to articular cartilage is usually permanent. In general, once damaged, therapy is normally directed at limiting or reducing joint inflammation, limiting the release of inflammatory mediators, removal of the inciting cause (e.g., the chip) and replacement of synovial fluid components. These measures are combined with a period of rest to allow for healing and fibrocartilage deposition at the affected area. The long term therapeutic objective is directed at slowing the progression of degenerative processes and controlling the clinical signs of DJD. Prevention is often aimed at limiting joint inflammation before damage to cartilage occurs and in providing proper nutritional support.
The treatment of connective tissue afflictions can be quite problematic. A simple decrease in the stress to which the connective tissue is subjected is often not an option, especially in the case of athletes and animals such as race horses. Consequently, treatment is often directed at controlling the symptoms of the afflictions and not their causes, regardless of the stage of the degenerative process. Presently, steroids, such as corticosteroids and NSAIDs, are widely used for the treatment of these ailments (Vidal, et al., Pharmocol. Res. Commun., 10:557-569 (1978)). However, drugs such as these, which inhibit the body's own natural healing processes, may lead to further deterioration of the connective tissue.
Connective tissue, for example articular cartilage, is naturally equipped to attempt to repair itself by manufacturing and remodeling prodigious amounts of collagen and proteoglycans (PGs). This ongoing process is placed under stress when an injury occurs. In such cases, the production of connective tissue matrix (collagen and proteoglycans) can double or triple over normal levels, thereby increasing the demand for the building blocks of both collagens and proteoglycans. The building blocks for collagen are amino acids, especially proline, glycine and lysine. Proteoglycans are large and complex macromolecules comprised mainly of long chains of modified sugars called glycosaminoglycans (GAGs) or mucopolysaccharides. The terms glycosaminoglycans and mucopolysaccharides are understood in the art to be interchangeable. Due to their dense negative ion content, proteoglycans molecules are able to attract and retain water within the cartilage formation specifically for lubrication. Proteoglycans provide the unique mechanical properties for flexibility, resiliency, and resistance to and recovery under compressive forces.
Glucosaminoglycans are polysaccharides which occur widely in the animal kingdom. Glucosaminoglycans that are present in the tissues of vertebrate animals have mainly a linear structure which is repetition of a disaccharide units composed of two monosaccharides. Five kinds of glucosaminoglycans are found in the tissues and fluids of vertebrates: chondroitin sulfates, keratin sulfates, dermatan sulfates, heparin sulfates, and hyaluronic acid.
Proteoglycans and collagen are the chief structural elements of all connective tissues. Their synthesis is essential for proper maintenance and repair of connective tissues. In vitro, the introduction of glucosamine, a key precusor for GAGs, has been demonstrated to increase the synthesis of collagen and GAGs in fibroblasts. In vivo, topical application of glucosamine has enhanced wound healing. Glucosamine has also exhibited reproducible improvement in symptoms and cartilage integrity in humans with osteoarthritis (L. Bucci, Nutritional Supplement Advisor, July 1992)).
The major proteoglycans found in cartilage are chondroitin sulfate, dermatan sulfate, keratan sulfate and hyaluronic acid (also known as hyaluronan or HA). Heparin sulfate is also a proteoglycan, although it is not a component of articular cartilage. Newer names for proteoglycans sometime reference function of the core protein within the molecule found in chondroitin sulfate and keratin sulfate, e.g., aggregan, a large proteoglycan aggregates with hyaluronin, or reference location (e.g., decorin (dermatan sulfate), which decorates type I collagen fibrils), or reference primary structure, biglycan which has two glysoaminoglycan chains. Chondrocytes are active cells within the cartilage matrix, which manufacture new collagen and proteoglycan molecules while excreting enzymes, which aid in removal of damaged cartilage and proteoglycans.
Chondroitin sulfate is broken down into sulfate disaccharides and N-acetyl galactosamine. D-Glucuronic acid is a key substrate comprising one half of the hyaluronan molecule, the other being N-acetyl D-glucosamine. Chondroitin sulfate, as CS4 and CS6 within the body, is thought to be an essential glycosaminoglycan which binds water to the articular cartilage matrix and is necessary for the formation of proteoglycans.
In particular, chondroitin sulfate is a long hydrophilic chain of repeating sugars. This glycosaminoglycan binds to proteoglycan molecules aiding in water and nutrient transportation within the articular cartilage. Chondroitin in its sulfate form includes galactosamine, a primary substrate of hylauronan and a disaccharide pathway for proteoglycan synthesis secondary to the hexosamine pathways utilized for glycosaminoglycan production. Chondroitin sulfate chains comprise the space formation of the cartilage matrix and integral parts of the proteoglycan molecule. Chondroitin stimulates the production of proteoglycans, glycosaminoglycans, and collagen, which are the building blocks of healthy cartilage. Chondroitin sulfate also inhibits the secretion of degenerative enzymes by the chondrocytes within articular cartilage. Chondroitin sulfates are non-toxic and work synergistically with glucosamine to hydrate and repair articular cartilage.
Hylauronan is an integral part of both synovial fluid and articular cartilage. Within the articular cartilage, hylauronan provides viscoelastic properties allowing ease of motion between opposing surfaces and increasing compressive resistance. Within the synovium, hylauronan, as a component of synovial fluid, provides an effective barrier regulating the introduction of plasma components. Under normal conditions, the body will synthesize sufficient amounts of base components to maintain and grow healthy articular cartilage, while limiting the production and release of destructive proteinases, inflammatory mediators and catabolic enzymes.
Glucosamine, as glucosamine 5-phosphate, is naturally occurring within the body and is a component in the biosynthesis of glycosaminoglycans, proteoglycans, hyaluronan, and collagen. Glucosamine is available in exogenous forms, glucosamine sulfate sodium, glucosamine hydrochloride and N-acetyl D-glucosamine. N-acetyl D-glucosamine is also a derivative of glucose obtained by chemical hydrolysis of chitin. This polysaccharide is readily soluble in water and extremely bioavailable. N-acetyl D-glucosamine binds to glucuronic acid as well as galactose making it a precursor to hyaluronic acid, keratan-sulfate and chondroitin sulfate. This unique derivative aids in proteoglycan, collagen and glycosaminoglycan production. N-acetyl D-glucosamine has also been shown to aid in the healing of soft tissue injury.
There have been countless therapeutic approaches for management of joint disease, providing nutritional supplementation of metabolic precursors to the diet to aid in the biosynthesis of proteoglycans, GAG's, hyaluronan, and collagen (see, U.S. Pat. Nos. 5,364,845 and 5,587,363). Numerous other disclosures also suggest the introduction of nutritional supplements as therapy for the treatment of connective tissues. For instance, U.S. Pat. No. 3,683,076 to Rovati et al. teaches that glucosamine sulfates are useful to treat arthritic conditions. U.S. Pat. No. 3,697,652 to Rovati et al. discloses that N-acetyl glucosamine can be used to treat degenerative afflictions of the joints. U.S. Pat. Nos. 5,364,845, 5,587,363, 6,492,349, 6,271,213, and 6,583,123 to Henderson et al. teach that glucosamine, chondroitin, manganese, and/or S-Adenosylmethionine (SAM) are used to protect and repair connective tissue. U.S. Pat. No. 6,632,804 to Ekanauake teaches that ferrous ion and an ascorbate, and glucodamine derivative are useful in treating osteoarthritis. U.S. Pat. No. 6,645,948 to Prtito et al. teaches a nutritional composition for treating connective tissue including a glucosamine salt, chondroitin sulfate, collagen and sodium hyaluronate.
In U.S. Pat. No. 5,840,715 to Florio, N-acetyl glucosamine sulfate, chondroitin sulfate, gamma linolenic acid ercosapentaenoic acid and docosahexaneoic acid, and manganese aspartate are combined to treat arthritis symptoms. U.S. Pat. No. 5,916,565 to Rose et al. teaches a composition comprised of D-glucosamine hydrochloride, chondroitin sulfate, cayenne, ginger, turmeric, yucca, Devil's Claw, nettle leaf, Black Cohosh, alfalfa, and celery seeds to repair and maintain damaged tissues in joints of vertebrates. In U.S. Pat. No. 5,922,692, Marino discloses that glucosamine sulfate and chondroitin sulfate can be added to foodstuffs. Additional related art discloses pharmaceutical compositions and methods for the treatment of connective tissue in humans and animals, such as U.S. Pat. Nos. 4,216,204, 4,782,046, 4,808,576, 4,837,024, 5,141,928, 5,840,715, 5,442,053, and 5,929,050.
While all the above references have been described as being effective for their intended use, there remains a need in the art for a therapeutic composition which demonstrates enhanced effectiveness in the treatment of connective tissues, exhibit other improved beneficial properties, and provides even wider applications in the modes of administration. The present invention meets these needs at least in part.